The Principle of Breakover Conduction

A DIAC is an Electronic Breakover Conduction Device

A DIAC is a two-terminal bidirectional switching device that opens and closes automatically. The physical property that turns ON a DIAC is called breakover conduction. A DIAC switches ON when its rated voltage is applied. A DIAC has a rated current and a minimum "holding" current. When the current drops below the holding current, the DIAC turns off.

Breakover Conduction

Breakover conduction is utilized in DIACs and gas discharge devices. At low voltage, a breakover conduction device exhibits high impedance (i.e. a capacitive characteristic). As voltage is applied across a breakover device, it remains at high-impedance up to the device's breakover voltage rating .  Once the device's breakover voltage is exceeded, the device switches to a low-impedance state, and current will flow. The following figure illustrates a DIAC VI curve.

DIAC VI Curve